Proceedings of The Physiological Society

Sleep Sleep and Circadian Rhythms (London, UK) (2018) Proc Physiol Soc 42, SA10

Research Symposium

Sleep in space

C. Tsai1,2, H. Hasegawa1,3, T. Morris-Paterson4, S. Higgins1,2, A. Keyoumars1,3, D. Green4,5, P. Goadsby6, G. D. Leschziner1,2, S. Harridge4, I. Rosenzweig1,2

1. Sleep and Brain Plasticity Centre, Department of Neuroimaging, King's College London, London, United Kingdom. 2. Sleep Disorders Centre, Guy's Hospital, London, United Kingdom. 3. Department of Neurosurgery, King's College Hospital, London, United Kingdom. 4. Centre of Human and Applied Physiological Sciences, King's College London, London, United Kingdom. 5. KBRwyle, European Astronaut Centre, European Space Agency, Cologne, Germany. 6. NIHR, Wellcome Trust King's Clinical Research Facility, London, UK, United Kingdom.

With rapid scientific development and interest in interplanetary travel in the 20th century, there has been an increasing focus on the effects of spaceflight and microgravity on human physiology. Whilst the effects of spaceflight on cardiovascular and respiratory physiology are well recognized, the effect on the brain has not been widely studied. Astronauts have long been reported to experience impairments in sensorimotor function including posture control, spatial orientation, manual tracking, and cerebellar dysfunction. Significantly shortened and disrupted sleep has also been consistently reported in space missions. Sleep serves a restorative function for the brain and cognition and involves dramatic changes to our perception, consciousness, cognition and health. The perpetual activity of the brain is largely supported by a variety of oscillations and rhythms it generates. Sleep and sleep stages are also characterized by specific brain oscillations, which, unlike those of wakefulness, are maintained free of external inputs. This means that a transient perturbation during sleep can have a lasting impact. Recent studies on astronauts have shown that weightlessness induces neurophysiological changes including a cephalic fluid shift which alters cerebrospinal fluid volume, cerebrovascular flow and autoregulation, and intracranial pressure. These changes may also induce various neuroplastic changes and significant structural and functional remodeling in the central nervous system including the effect on the oscillations of sleep, positing that spaceflight might be associated with structural, functional and cognitive deficits of, as of yet unclear, longer-term impact. In that background, the results of our recent study that investigated the effects of seven days of supine unloading on a hyper-saline filled water bed (hyper buoyancy floatation), a novel Earth-based novel analogue of microgravity will be discussed. In our study, twelve healthy male subjects (flotonauts), aged (27.2±4.2 years), with no previous neuro/psychiatric history, underwent a multimodal imaging and an overnight in-laboratory polysomnography (PSG/EEG) recordings during seven days of an unloading period. For the duration of the intervention period, the subjects lied supine, followed controlled sleep/wake schedules, they were fed a controlled diet and allowed a maximum of 15 minutes per day off the hyper buoyancy floatation bed (for personal hygiene etc). Several significant changes in sleep rhythms were found, with associated changes in neuroanatomy, cognition and neuroelectrical activity and connectivity. These changes will be presented with particular emphasis on changes in slow oscillations during sleep, which have recently been associated with amyloid load in the brain. The proposed underlying mechanisms will be discussed in some detail.

Where applicable, experiments conform with Society ethical requirements